Which Seaweed is Most Protective Against Breast Cancer?

Unfortunately, as the traditional diets of East Asia have westernized, their breast cancer rates have risen, which some have linked to a quadrupling of animal product consumption.This is the breast cancer rate of Japanese women living in Japan. If they emigrate to the United States, within 10 years, they’re up to here, and if they hang around long enough, here’s the risk of resident Japanese Americans living in the United States. Note, though, that it’s still somewhat lower than the U.S. national average. This may be because of some of the dietary habits they carry with them, soy consumption, green tea, maybe eating more mushrooms, but maybe partly it’s the seaweed.

We’ve known for over a decade that in vitro, in a Petri dish, seaweed broth is effective at clearing cancer cells. Here are three different types of human breast cancer, measuring cancer cell death. Here’s what a widely used chemotherapy drug can do, and here’s seaweed. It worked even better, and unlike the chemo, it didn’t hurt normal, non-cancerous breast cells.

What about outside of the test tube, in people? Well, a population study comparing women with breast cancer to women without found that consuming a single sheet of nori a day may cut a woman’s odds of breast cancer in half. We think it’s because seaweed favorably alters estrogen metabolism, likely due to modulating women’s gut bacteria. See, the more seaweed you eat, the less estrogen you have in your system, which may lower breast cancer risk.This may be because of all the fiber in sea vegetables, or it may block the enzyme that undermines our body’s attempt to flush out excess hormones, or even somehow interfere with estrogen binding to estrogen receptors. Whatever the cause, to effectively lower their estrogen levels, Asian women may be able to get away with about one sheet of nori a day, but American women are so much bigger that it may take closer to two.

There are lots of yummy seaweed snacks out there to make it a tasty experience—just try to get some low-fat, low-sodium ones.”Walk-ka-may,” the seaweed used fresh in seaweed salads, unfortunately did not appear to reduce breast cancer risk, though it has been found to rather dramatically lower blood pressure in hypertensives, people with high blood pressure. Just two teaspoons of seaweed salad a day for a month dropped their blood pressure 14 points and after two months was associated with up to a 2 inch skinnier waistline.

As I’ve mentioned before, though, I’d recommend avoiding hijiki, which tends to have too much arsenic, and kelp, which tends to have too much iodine. In fact, too much seaweed of any type may actually increase one’s risk for thyroid cancer because of the amount of iodine you’d be taking in, but there does not appear to be increased risk at the levels of consumption I’m talking about, like a sheet of nori every day. And a study of seaweed eaters in California actually found decreased risk, but, again, we’re talking modest levels of intake.

You know I’ve frequently talked about the benefits of dietary diversity, eating different families of fruits and vegetables, eating different parts of individual plants—beets, and beet greens. If we just stick to land plants, though, we’re missing out on all the plants from the other 70% of planet earth. Sea vegetables have phytonutrients found nowhere else, types of fiber, and unique carotenoids, and polysaccharides, and various polyphenol defense compounds, each of which may have anti-cancer properties. I encourage everyone to try experimenting until you find one you like, even if that means just sprinkling some powdered dulse on your food.

About Michael Greger M.D.Michael Greger, M.D.S, is a physician, author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous “meat defamation” trial. Currently Dr. Greger proudly serves as the Director of Public Health and Animal Agriculture at the Humane Society of the United States.

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